DNA methylation-mediated silencing of genes has been implicated in the pathogenesis of many diseases including cancer. Hsiao et al., Semin Cancer Biol, 19 p. 198-208 (2009). Since the discovery that DNA methylation-mediated gene silencing is a reversible event, identifying small-molecule DNA methylation inhibitors, either natural or synthetic, for cancer treatment has been the focus of significant investigation. Yoo, C. B. and P. A. Jones, Nat Rev Drug Discov, 5(1), p. 37-50 (2006). Among many agents with DNA methylation-modifying capability, 5-aza-2′-deoxycytidine (decitabine; 5-Aza) is the best-known DNA demethylation agent. 5-Aza exerts its effect by inhibiting DNA methyltransferases (DNMTs), the key enzymes responsible for initiating or maintaining the DNA methylation status, thereby facilitating the re-expression of tumor suppressor genes through DNA hypomethylation. Its therapeutic efficacy is manifest by the Food and Drug Administration approval for the treatment of myelodysplastic syndromes. While 5-Aza is a potent DNA demethylation agent, its use is associated with increased incidences of bone marrow suppression, including neutropenia and thrombocytopenia, due to the disruption of DNA synthesis. Chuang et al., Mol Cancer Ther, 4, p. 1515-20 (2005). In addition, shorter half-life hinders the effective delivery of 5-Aza to the tumor site.
Recently, procainamide has emerged as a potential DNA demethylating agent for clinical translation. Evidence indicates that procainamide inhibits DNMT1 by reducing the affinity with its two substrates: hemimethylated DNA and S-adenosylmethionine. Lee et al., J. Biol Chem, 280, p. 40749-56 (2005); Lin et al., Cancer Res. 61, p. 8611-6 (2001); Lu et al., J. Immunol. 174, p. 6212-9 (2005). Through DNA demethylation, procainamide causes growth arrest (Villar-Garea et al., Cancer Res. 63, p. 4984-9 (2003)) and reactivation of tumor suppressor genes in cancer cells. Segura-Pacheco et al., Clin Cancer Res, 9, p. 1596-603 (2003). Moreover, as an anti-arrhythmic drug, procainamide has a well-characterized safety profile without side effects commonly associated with nucleoside analogues. Martelli et al., Toxicol. Appl. Pharmacol. 131, p. 185-91 (1995); Mereto et al., Toxicol Appl Pharmacol. 131(2), p. 192-7 (1995). However, in contrast to 5-Aza, procainamide requires high concentrations (≧50 μM) to be effective in DNA demethylation in suppressing cancer cell growth. Lee et al., J. Biol. Chem. 280, p. 40749-56 (2005). Accordingly, there remains a need for additional DNA methylation inhibitors, particularly those with greater potency or lower cytotoxicity.